Coil having heat conductive segments and c-shaped conductive path



Sept 22 1964 A. P. wlLsKA 3 15 COIL HAVING HEAT coNDUcTIvE sEGMENTs 0339AND C-SHAPE CONDUCTIVE PATH Filed July 5, 1962 A rroA/EYS United StatesPatent O 3,150,339 COIL HAVlNG HEAT CONDUCTIVE SEGMENTS AND C-SHAPED`CNDUCTIVE PATH Alvar P. Wilska, Tucson, Ariz., assignor to PhilipsElectronics and Pharmaceutical Industries Corp., New York, N.Y., acorporation of Maryland Filed `Iuly 5, 1962, Ser. No. 207,707 2 Claims.(Cl. 336-61) This invention relates to an electrical coil for producinga concentrated magnetic field. In particular, it relates to a coilsuitable for use in electron beam focusing devices and not requiringferromagnetic material to concentrate the magneticeld.

It isY frequently desirable to produce strong magnetic fields inconcentrated spaces, `particularly in devices making use of electronbeams, such as electron microscopes and traveling wave tubes andthelike. It has long been known that magnetic elds may be produced by thepassage of an electric current through a conductive coil and that suchfields can be concentrated or shaped to a limited extent by shaping thecoil itself. However, it has been thought heretoforethat, in order tohave a very highly concentrated magnetic eld produced by currentVflowing through :a coil, the coil would :have to be ywound n, orassociated closely with, a ferromagnetic core structure.

In certain electron beam devices, particularly electron microscopes, theinhomogeneities of a ferromagnetic core structure introducedistortions-in the magnetic field that result in unacceptabledistortions of the beam. These inhomogeneities are yat least partlydetermined by the crystalline structure of the ferromagnetic materialand are not systematic and cannot be completely corrected.

Furthermore, hysteresis effects in ferromagnetic matevrial makes itditlicult to control variations in the magnetic intensity to the preciseamount that is frequently required. One reason is that the hysteresiseffect results in a nonlinear variation of the magnetic eld, even if theelectric current in the associated coil can be varied linearly. Foranother thing, the domains of the ferromagnetic particles shiftabruptly. In addition, the non-linearity is made worse by the fact thatferromagnetic materials become saturated when the magnetic ilux exceedsa certain amount, depending on the volume of ferromagnetic materialinvolved.

The present invention comprises a coil capable of producing highlyconcentrated magnetic elds Without ferromagnetic material. The coil ismade up of individual, conductive layers each of which is in the form ofa conductive sheet with an almost-closed circuit surrounding an innernon-conductive, or open, space. The edges of the sheet extend outwardlyfrom the circuit and are formed integrally therewith by means of slotsextending from the edge of the sheet in toward the circuit. Any numberof these layers may be stacked together, but they must be insulated fromone another, and also in accordance with the present invention, thisinsulation may be in the form of a 'thin layer of material, such asevaporated silicon dioxide. In order to connect the layers together, alimited area at the end ofthe circuit on one side of the sheet is keptfree of insulating material and is covered instead with solder or thelike so that the layers may be stacked together and heatedsimultaneously to cause the solder at one end of each circuit to becomeattached to the other end of the circuit of the next adjacent layer.

The inven-iton will be described in greater detal in connection with thedrawing, in which:

FIG. 1 shows a single layer of -a coil constructed according to theinvention;

FIG. 2 shows an enlarged cross-sectional view of the layer in FIG. ltaken along the line 2 2;

3,150,339 Patented Sept. 22, 1964 ice FIG. 3 shows an enlargedcross-sectional view of a. stack of such layers; and

FIG. 4 shows a coil constructed in accordance with FIG. 3 expandedaxially.

The coil layer in FIG. l comprises a sheet 11, which in this case is acircular sheet of conductive material, such as copper. The sheet mayhave any desired thickness; in a particular embodiment, I have used asheet having a thickness of approximately Zmils. The sheet has a C-shaped, conductive path or circuit 12 defined by an open inner area 13and, less explicitly, by the inner ends of a plurality of slots 14spaced around the sheet. The slots 14 may be spaced at approximatelyequal angles, although this is not necessary, .and normally they extend`approximately radially in toward the center of the area 13.

In order to deiine a conductive path 12, the slots 14 extend only partway from the edge of the sheet 11 toward the open area 13. However, oneslot 16 extends all the way in to theopen area to give the conductivepath 12 a C-shaped configuration so that it will not be selfshortcircuiting. `Electrical connections may be `made to the path 12 bymeans of the segments 17 4and 18 lying on each side of the slot 16.

Alternatively, and particularly if a number of sheets, such as sheet 11,are to be connected together, a small area 19 at one end of eachconductive path 12 on each of the sheets may be provided with aconductive material, such as a 10W melting point solder, to `permit thesheets to be stacked together and then hea-ted to melt the solder oneach layer to make it adhere to the' adjacent layer. Preferably, alimited solder area 21 is `also provided on the other side of the sheet11 at the other end of the conductive path 12.l

' In order to stack a multiplicity of sheets 11 together,

or even to permit a single sheet to be attached to a conductive body, itis` desirable to insulate the surface of the sheet. FIG. 2 shows a layerof insulating material 22 on the surface of the sheet 11. In the examplereferred to `above of a 2mil sheet 11, it was found that a layer ofevaporated silicon-dioxide approximately l0 microns thick was suilicientto insulate the copper.

In order to connect the sheets together electrically, the insulatingmaterial 22 must be kept off of, or removed frorn, a limited area at oneend of the C-shaped path 12 (FIG. l). This may be done by masking asmall area of the sheet 11 at the time the insulating material isapplied and then later removing the mask and applying a small amount ofmetal that melts at a low temperature. For example, a small quanti-ty oftin may be evaporated onto the area 19.

When a plurality of sheets 11 is to be connected together in a stack, asindicated in FIG. 3, it is necessary to arrange the sheets so that thelow-melting-temperature metal at one end of the conductive C-shaped pathof one sheet will join with the low-melting-temperature metal at theother end of the next adjacent sheet. This is indicated in FIG. 3 by thejunction between the area 21a of sheet 11a, which is directly in contactwith and is`fused to the area 19h of sheet 11b. Upon reflection it willbe apparent that the points of contact are not in a straight line andtherefore in the two sheets 11c and 11d at the other end of the stackthe corresponding areas 21c and 19d are angularly displaced from theareas 21a and 19b.

FIG. 4 shows an expanded spiral made up of a number of sheetscorresponding to sheet 11. Normally, of course, the layers of such aspiral would not be spread apart; this is done here only forillustrative purposes. As may be seen, the slots 14 of the variouslayers need not Abe aligned with one another, so that the whole stackforms something approaching a monolithic conductive block which servesas an excellent heat conductor to carry heat away from the area wherethe electrical current is flowing, i.e. in the inner C-shaped path 12 ofeach layer. Because of thehintegral formation of the conductive path 12and the outer segments of each sheet, these outer segments are welladapted to serve as cooling fins to carry heat away from the conductivepath portion 12. However, the electrical current will not fow Vacrossthe slots 14 and is, therefore, confined substantially entirely to theconductive path 12. Even if the current fringes slightly into the outersegments, it will not adversely affect the shape of the magnetic fieldto any significant degree and may be easily compensated for.

In the case of a 90.layer coil made up of 2-rnil sheets, I have found itpossible to obtain a mm. focal length in an electron beam accelerated to10,000 volts with'a temperature rise in the coil of only approximately 4C. above ambient temperature, even though the heat radiated by the coilamount to 36 watts. The number of ampere turns was 1,000. The same coiloperated with a beam accelerated to 90,000 volts, and with the coilsdissipating 108 watts with 3,000 ampere turns, had a temperature rise ofonly approximately 12 C. above ambientV temperature.

While this invention hasbeen described in terms of a particularembodiment, it will be Vrecognized by those skilled in the art thatmodifications may be made therein without departing from the true scopeof the invention as defined by the following claims.

What is claimed is:

1. A coil comprising a plurality of turns, each of said turns comprisinga circular sheet of conductive non-ferromagnetic material having acentral aperture therein; a first slot extending from the edge of saidcircular sheet to said aperture; a plurality of other V-shaped slotsextending from the edge of said sheet part of the way in toward saidaperture, said other slots being spaced substantially equi-distantlyaround said sheet and leaving a C-shaped, conductive path surroundingand defining said aperture with the ends of said C-shaped, conductivepath bounding and defining the innermost ends of said one slot; a rstsolder layer in a limited region at one end of said C- shaped,conductive path on one surface of said sheet; a second solder layer in asecond limited region on the other surface of said sheet at the otherend of said C-shaped, conductive path; and an insulating layerintimately attached -to and covering both surfaces of said sheet exceptfor each of said solder layers, the first solder layer of each of saidturns being fused to the second solder layertof the adjacent turn, saidturns being in `surface-to-surface contact to form a monolithic, hollowair-core coil.

2. A coil comprising a plurality of turns, each of said i turnscomprising a circular sheet of conductive non-ferromagnetic materialhaving a central aperture therein; a first slot extending from the edgeof said circular sheet to said aperture; a plurality of other V-shapedslots extending from the edge of said sheet part of the way in towardsaid aperture, said other slots being spaced substantiallyequi-distantly around said sheet and leaving a C-shaped, conductive pathsurrounding and defining said aperture with the ends of said Clshaped,conductive path bounding and defining the innermost ends ofV said oneslot; a first solder layer in a limited region at one end of saidC-shaped, conductive path on one surface of said sheet; a second solderlayer in a second limited region on the other surface of said sheet atthe other end of said C-Shaped, conductive path; and a layer ofevaporated silicon dioxide intimately attached to and covering bothsurfaces of said sheet except for each of said solder layers, the firstsolder layer of each of said turns being fused to the second solderlayer of the adjacent turn, said turns being in surface-to-surfacecontact to form a monolithic, hollow air-core coil.

References Cited in the file of this patent UNITED STATES PATENTS267,138 Blanchard Nov.Y 7, 1882 1,385,624 VKent n July 26, 19211,801,214 Von Henke Apr. 14, 1931 1,882,201 V Taetz Oct. 11, 1932l2,061,388 Schou Nov. 17, 1936

1. A COIL COMPRISING A PLURALITY OF TURNS, EACH OF SAID TURNS COMPRISINGA CIRCULAR SHEET OF CONDUCTIVE NON-FERROMAGNETIC MATERIAL HAVING ACENTRAL APERTURE THEREIN; A FIRST SLOT EXTENDING FROM THE EDGE OF SAIDCIRCULAR SHEET TO SAID APERTURE; A PLURALITY OF OTHER V-SHAPED SLOTSEXTENDING FROM THE EDGE OF SAID SHEET PART OF THE WAY IN TOWARD SAIDAPERTURE, SAID OTHER SLOTS BEING SPACED SUBSTANTIALLY EQUI-DISTANTLYAROUND SAID SHEET AND LEAVING A C-SHAPED, CONDUCTIVE PATH SURROUNDINGAND DEFINING SAID APERTURE WITH THE ENDS OF SAID C-SHAPED, CONDUCTIVEPATH BOUNDING AND DEFINING THE INNERMOST ENDS OF SAID ONE SLOT; A FIRSTSOLDER LAYER IN A LIMITED REGION AT ONE END OF SAID CSHAPED, CONDUCTIVEPATH ON ONE SURFACE OF SAID SHEET; A SECOND SOLDER LAYER IN A SECONDLIMITED REGION ON THE OTHER SURFACE OF SAID SHEET AT THE OTHER END OFSAID C-SHAPED, CONDUCTIVE PATH; AND AN INSULATING LAYER INTIMATELYATTACHED TO AND COVERING BOTH SURFACES OF SAID SHEET EXCEPT FOR EACH OFSAID SOLDER LAYERS, THE FIRST SOLDER LAYER OF EACH OF SAID TURNS BEINGFUSED TO THE SECOND SOLDER LAYER OF THE ADJACENT TURN, SAID TURNS BEINGIN SURFACE-TO-SURFACE CONTACT TO FORM A MONOLITHIC, HOLLOW AIR-CORECOIL.